Geiger-muller counter tube



Oct. 2,.1956 P. B. WEISZ GEIGER-MBLLER COUNTER TUBE Filed Sept. 30, 1952 INVENTOR. Pam! J ii wz BY ATTORNEY United States Patent 2,765,418 GEIGER-MfiLLER COUNTER Paul B. Weisz, Pitman, N. J5, assignor' to So'cony Mobil Oil Company, Inc'., a corporation-offNew York ApplicationSeptemben30; 1952,.Serial=.No; 312,203-

3 Claims. (Cl. 31393) In the. fabrication of Geiger-Muller counter tubes one of the components, sometimes the characteristic component, of the gaseous atmosphere: utilized is a hydrocarbon.

For example, in my prior patent, U. S.--Platent- 2,519,864, the use of gaseous fillings. comprising; hydrocarbons of the series CnH2n+2 and CnHZn is shown; where n. is from 2 to 8,. inclusive, and .the hydrocarbon makes up from 0.1% to 6%, approximately; of the total gaspressure'. The other constituent of the: disclosed atmosphere. may be hydrogen, nitrogen, argon; neon, helium, etc...

Such fillings are of value for numerous. reasons, butit has been observed that the use of hydrocarbon gases in closed counter tubes has resulted in relatively small life-time (frequency approximately 10 counts), the operation being limited by the formation of deposits. In tubes wherein the filling gas is continuously flowed through the tubes, tubes filled with mixtures comprising hydrocarbons have been used with considerable commercial success without experiencing deterioration of the counting characteristic of the tube assembly. It appears that in many cases the deposits involve decomposition products of the filling gas.

While my prior patent discloses the use of olefinic gaseous hydrocarbons, it remarks that they are not to be preferred since, when they were used the life-time of the tubes is unpredictable. It is believed that this is due to the formation of polymerization products.

This invention has for its object the provision of a Geiger-Muller counter tube assembly, closed in type, including a hydrocarbon filling gas, which has a greatly increased life-time and a substantially lessened tendency for the formation of deposits involving decomposition products of the filling gas.

It has for an object the provision of a closed type Geiger-Muller counter tube having a life expectancy and ability to maintain operating characteristics of the order of those obtained in a continuously streamed tube (where gas is flowed through), employing a filling of similar character comprising a hydrocarbon.

It has for another object the lessening of depositions formed within Geiger-Muller type counter tubes, from decomposition products of filling gases.

These and other objects may be obtained by the invention herein disclosed and claimed, which is based upon the discovery that the formation of decomposition products in the presence of hydrocarbon filling gases may be prevented by providing conditions suitable for the suppression of the formation of olefinic constituents and their subsequent polymerization to materials of higher molecular weight.

This invention involves the incorporation in a hydrocarbon filled closed tube Geiger-Muller counter of a hydrogen donor, usually gaseous hydrogen, and a material which is catalytically active to continually catalyze the hydrogenation of unsaturated hydrocarbons.

For example, it is now well known that such catalysts as metallic nickel as Well as other elements of group 2,765,418 iiatented- Oct. 2,1956

of' the periodic system are: capable of initiatingthe hydrogenation of'hydrocarbons at temperatures" as low as room temperature. In addition to this, the mole quan= tities which are involved and the rate at'which they need to be removed are extremely small, and only slight 'cata lytic action is necessary to accomplish the removal of traces of unsaturated hydrocarbon; The approximate magnitude of unsaturated" hydrocarbon gases'in' a counter tube' constructedaccordingto my prior patent and hav ing in itsinitial filling onlysaturated hydrocarbons ap pears to be of the order of about 10- moles per operating day" or even less.- Active-- nickel has been reported to have velocity constants for hydrogenation of the order of 10- moles per second persquare-centimeter of catalyst surface at 0 C. Obviously, a properly activated nickel surface of a-few square centimeters will be suflicient to accomplish the d esired conversion.

According to one form of this invention, Geiger tubes are made of otherwise standard construction but incorporating at least some 10 or more sq; cm. of metallic ni-ckelwh'ich inthe course of manufacture and preparation of gasfilling of said tubes is catalytically activated by chemical reduction in the presence of hydrogen, and these-tubes are filled with .ahydrocarbon mixture to which isad'd edhydro gen. An-exam'pleisas follows: Nickel is introduced as the material of the-cathode cylinder in the constructionof 'thetube. The tube is then heated to a temperature-of approximately 400-500 'C. in the presence of an atmosphere of hydrogen within the tube for aperiod of about one hour. The hydrogen is then evacuated and the gaseous mixture is admitted consisting of approximately 200 mm. of hydrogen, 400 mm. of argon and approximately 1 to 5 mm. butane. Since some substances such as oxygen, sulphur and the like diminish or poison the catalytic activity of the metallic catalyst, every effort should be made to exclude these from the final filling. Oxygen, being the most likely poison, the inert gas and hydrocarbon filling should be treated to remove it, as by passing the inert over reduced copper, and by using hydrocarbons which have been subjected to redistillation. The tube is sealed off after filling.

The catalyst metal may be any of the usually used metallic hydrogenation catalysts, preferably nickel or platinum, and usually, nickel. It may be utilized either as one of the structural elements of the tube, for examplc the cathode cylinder, or in a tube having a metal wall, the wall may be of nickel. Or, other functional portions of the structure within the tube may be made of nickel. It may also be desirable, where the nickel is not so used to introduce it as powder, turnin-gs, gauze or other form, placed within the tube so as to be accessible to the gas filling therein without being so placed as to interfere with the gas discharge.

Whatever the catalyst metal is, it is essential that it be in an active reduced state. Consequently an essential element of the preparation of a counter tube in accordance with my invention is the reducing, in situ, of the metal, before final filling and sealing off of the tube. Temperatures at which such reduction may be accomplished are well known, as are many reducing atmospheres which may be used. Of these, since it is to be used as a part of the final filling, hydrogen is obviously the most convenient. Concurrent with this is provision of a filling free from oxygen and similar poisons.

In order that this invention may be visualized, reference is now made to the single figure of the drawing which is attached to and made a part hereof. In this drawing, 1 denotes the shell of the Geiger-Muller counter tube, having a cylindrical cathode 2, made of nickel and an anode wire 3. A connection tube 4 is provided, whereby the tube may be exhausted, provided with a desired atmosphere, etc., and which may be finally sealed when the tube is completed and filled. A means of I heating the interior metal parts must be provided, as for example, a means of inductive heating, such as that commonlyused in the getting or gas freeing of ordinary vacuum tubes, and is indicated diagrammatically by 5 and 6.

To finish the tube it is evacuated to a desired degree through 4 and then supplied with a hydrogen atmosphere and the metal parts, including specifically the nickel cathode 2 are inductively heated to about 400-500" C. for about one hour. Then the hydrogen is evacuated and the desired atmosphere, consisting of saturated hydrocarbons, inert gas, and hydrogen is introduced, after which 4 is sealed oif.

As disclosed in my prior patent, U. S. Patent 2,519,864, the desirable hydrocarbon constituents of a counter atmosphere are the hydrocarbons of the saturated series CnH2n+z where n is from two to eight, inclusive. The inert component may be any of the usually chosen inert components such as argon, helium, and the like.

I claim:

1. A Geiger-Muller counter tube comprising an envelope, a cathode and anode mounted within said envelope, an internal atmosphere comprising hydrogen and saturated hydrocarbons of low molecular weight and substantially free of unsaturated hydrocarbons, and having within said envelope an exposed surface of a reduced 3. That method for the manufacture of a Geiger-Muller counter comprising the steps of providing an envelope containing a cathode and an anode and in which there is a surface of a metal which when reduced is capable of catalyzing the hydrogenation of unsaturated hydrocarbons at low temperatures, filling the envelope with a reducing gas, heating the exposed surface of catalytic metal within said envelope in the presence of the reducmetal capable of catalyzing the hydrogenation of unsatu- I rated hydrocarbons at low temperatures.

2. The article of claim 1 in which the exposed metal surface is selected from the group consisting of nickel and platinum. V

ing gas, whereby the metal is reduced in situ, thereafter withdrawing the reducing gas, filling the envelope with an atmosphere comprising a saturated hydrocarbon of low molecular weight and hydrogen which atmosphere is substantially free of unsaturated hydrocarbons, and seal- References Cited in the file of this patent UNITED STATES PATENTS Lockwood Mar. 10, 1931 Fehr et al'. Sept. 30, 1952 OTHER REFERENCES 

